<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        /*标签选择器，选择页面上所有的标签*/
        div{
            width: 100px;
            height: 100px;
            background-color: red;
            /*solid: 实线*/
            border: 2px solid blue;
            padding: 10px;
        }
    </style>
</head>
<body>
    <div></div>
</body>
</html>